Eur J Vasc Endovasc Surg 19, 197–201 (2000)

doi:10.1053/ejvs.1999.0988, available online at http://www.idealibrary.com on

Dilatation of the Proximal Neck of Infrarenal Aortic Aneurysms afterEndovascular AAA Repair

J. J. Wever1, A. J. de Nie1, J. D. Blankensteijn∗1, I. A. M. J. Broeders1, W. P. Th. M. Mali2 andB. C. Eikelboom1

Departments of 1Vascular Surgery and 2Radiology, University Medical Center, Utrecht, The Netherlands

Objectives: to assess size changes of the proximal aortic neck after endograft placement.Methods: since 1994, 54 consecutive patients have undergone abdominal aortic aneurysm (AAA) repair with theEndovascular Technologies (EVT) endograft. The study group comprised the 33 patients who had completed at least sixmonths of the prospective follow-up protocol. The pre-, postoperative and follow-up helical computed tomography (CT)angiograms (CTAs) were processed on a workstation. The proximal neck dimensions were measured perpendicular to thecentral lumen line of the aortic neck. The cross-sectional area was measured at the proximal attachment system and at1 cm proximal to the renal arteries.Results: while the dimensions of suprarenal aorta did not change, a significant dilatation of the proximal neck was found.The median increase was 10.3% at 6 months and 15.5% at 12 months. No correlation could be found between the amountof dilatation and pre- or postoperative neck-size, graft diameter and amount of graft-oversizing.Conclusion: the infrarenal aortic neck demonstrates continued dilatation during follow-up after endograft placement.

Key Words: Abdominal aortic aneurysm; Endoprosthesis; Endovascular repair; Spiral computed tomography angiogram(CTA).

Introduction This study was performed to assess size changes of

the supra- and infrarenal aorta after endovascular

Long-term success after endovascular treatment of aneurysm exclusion, as measured along the central

lumen line on spiral CTA scans.abdominal aortic aneurysms depends on durable fixa-

tion of the endograft at the proximal and distal necks.

Gradual dilatation of the aorta at the level of at-

tachment systems may cause leakage and stent mi-

gration. Studies in healthy persons have shown that Patients and Methodsthe infrarenal aortic diameter increases 26% in males

and 24% in females between the age of 25 and 70 From January 1994 until November 1998, 54 con-

secutive patients underwent endovascular treatmentyears.1 After conventional abdominal aortic aneurysm

(AAA) repair higher rates of increase have been de- of an infrarenal aortic aneurysm, using the EVT Endo-

graft (Guidant, Menlo Park, CA, U.S.A.). Post-scribed.2–5

Some studies show dilatation of the proximal aortic operatively, all patients were subjected to contrast-

enhanced computed tomography (CTA) scanning atneck following endovascular AAA repair, but these

studies were performed on axial CT slices.6–8 Proximal discharge, 6 months, 12 months and yearly thereafter.

In 21 patients follow-up was less than 6 months dueneck measurements performed on linear reformats

perpendicular to the central lumen line are preferable. to operative mortality in one, non-related mortality in

one, conversion in six and duration in 10, while threeWith this method the position relative to the renal

arteries is not dependent on the slice thickness, and patients were followed in another hospital. The re-

maining 33 patients were included in the study. Intherefore the reproducibility is better.

these patients, 11 tube, 19 bifurcated and three aorto-

iliac endografts were implanted. There were four fe-∗ Please address all correspondence to: J. D. Blankensteijn, De-

male and 29 male patients. The median age was 69partment of Vascular Surgery, G.04.232, University Medical Center,PO Box 85500, 3508 GA Utrecht, The Netherlands. years (IQ range 63–73).

1078–5884/00/020197+05 $35.00/0 2000 Harcourt Publishers Ltd.

J. J. Wever et al.198

Table 1. Median cross-sectional area (IQ range) during follow-upin mm2.

Postoperative 6 months 12 months(n=33) (n=33) (n=24)

Proximal neck 346 (292–379) 365 (321–418)∗ 397 (309–439)∗Suprarenal 378 (340–423) 399 (331–440) 390 (342–442)

∗ p<0.01 Wilcoxon rank.

Table 2. Median of the individual changes (IQ range) comparedto the postoperative value.

6 months 12 months(n=33) (n=24)

Proximalneck +10.3% (+4.9%–+15.1%) +15.5% (+11.7–+24.4%)Suprarenal +1.1% (−4.5%–+5.4%) −3.2% (−6.9%–+4.1%)

Fig. 1. Drawing of the contour on the linear reformats. The cut-planeis always perpendicular to the vessel axis, providing a reproduciblemeasurement. 6–48). The median cross-sectional area showed a sig-

nificant increase at the level of the proximal attachment

system from 346 (292–379) mm2 to 365 (321–417) mm2

Preoperative, postoperative and follow-up contrast-at 6 months (p<0.01) and to 397 (309–438) mm2 at 12

enhanced CT images were reviewed on an Easy Visionmonths (p<0.01) compared to the postoperative area

workstation (Philips Medical Systems, Best, The Neth-(Table 1). The median increase between 6 and 12

erlands) to determine changes in cross-sectional areamonths was also statistically significant (p<0.05). The

of the abdominal aorta at the levels indicated below.median of the individual changes was +10.3% after

All measurements were taken perpendicular to the6 months and +15.5% after 12 months. These results

central lumen line.9–12 Proximal neck dimensions wereare shown in Table 2. The size changes at the level

measured 1 cm below the most distal renal artery. Onof the proximal attachment system in the individual

the preoperative scans, a contour was drawn outliningpatients are shown in Fig. 2. All but two patients

the aorta. On the postoperative scans this level allowedshowed an increasing cross-sectional area during fol-

measuring the neck in the proximal attachment system,low-up, compared to the first postoperative measure-

and the contour was drawn through the hooks (Fig.ment. In three patients, four years of CTA follow-up

1). The suprarenal aortic dimensions were measuredwas available demonstrating an increased neck-size of

in the same manner at 1 cm above the most proximal11.1%, 21.5% and 24.9% at 24, 36 and 48 months,

renal artery.respectively.

For statistical analysis the Wilcoxon rank test wasThe suprarenal aorta did not show significant

used to assess significance of postoperative and follow-growth (p>0.4) (Fig. 3). The individual neck-sizes on

up size changes. Correlation between the amount ofthe first postoperative scans were all smaller than the

dilatation and pre- and postoperative neck-size, graftnominal (maximal) size of the implanted stent graft,

diameter and amount of graft-oversizing was cal-due to intentional graft-oversizing. The median ratio

culated using Spearman’s test. A value of p<0.05 wasof oversizing was 1.13 (1.07–1.31). The amount of

considered statistically significant. All values are givendilatation did not correlate with preoperative neck-

as median and quartile range or as individual values.size (r=−0.12, p=0.50), postoperative neck-size (r=−0.25, p=0.16), nominal graft diameter (r=0, p=1.00)

or attachment system oversize (r=0.08, p=0.67). No

correlation with the presence of early (r=−0.09, p=Results0.59, n=14) or late endoleak (r=0.06, p=0.74, n=8)

could be demonstrated. Secondary endoleak or mi-The 6-month, 1-, 2-, 3- and 4-year follow-up scans

were available in 33, 24, nine, five and three patients gration was not encountered in the studied patient

group.respectively. Median follow-up was 12 months (range

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Proximal Neck Dilatation after Endovascular AAA Repair 199

Fig. 2. Cross-sectional area at the proximal aortic neck in the 33 patients. Size in square millimetres is indicated on the vertical axis, andfollow-up interval for each patient is indicated on the horizontal axis.

Discussion Matsumura et al.,13 no significant proximal neck growth

was demonstrated at 12 months. In their study, 34

The postoperative scan data demonstrate significant patients with an EVT endograft were analysed using

axial diameter measurements. One year later, the sameproximal neck dilatation at 6 and 12 months after

endovascular AAA repair. Comparison to the pre- authors reported on a larger group of patients (n=59)

and showed a mean increase of 0.7 and 0.9 mm inoperative scans was not performed because aortic neck

measurements with or without an EVT endograft in proximal neck diameter after 1 and 2 years re-

spectively.7 May et al.8 reported on increasing proximalplace are difficult to compare. The reason for this is

that artefacts caused by the stent material prevent neck diameters when comparing the preoperative val-

ues with the postoperative ones, but no progressivemeasurement of the aortic wall. Therefore, the area

within the stent was measured. For obvious reasons, increase at 6, 12 and 18 months. The diameters were

measured 1 cm below the renal arteries on axial CTthis measurement was not available from the pre-

operative scans. slices. They found no increase in aortic diameter at

the level of the coeliac trunk. The above-mentionedThe use of a workstation allowed measuring cross-

sectional areas. Other groups have studied the changes studies are difficult to compare, as various stent-graft

designs were used.in diameter and circumference but the reproducibility

of these measurements is limited in case of irregular Two possible explanations can be given for continued

growth of the infrarenal neck after endovascular AAAcontours of the proximal neck. Using callipers, Sones-

son et al.6 measured diameters on axial CT planes in repair. It is either a continuation of the aneurysmal dis-

ease process or an effect of the outward force generated31 patients treated with a home-made stent graft. They

found a significant mean increase of 1.7 mm at the last by theendovascular stentonto the infrarenalaortic wall.

Although it is most probably a combination of theseavailable follow-up scan compared to the preoperative

neck-size. In addition an insignificant mean increase two factors, it is interesting to discuss these issues sep-

arately, as the proximal attachment mechanisms varyof the suprarenal aorta was found. In the study of

Eur J Vasc Endovasc Surg Vol 19, Month 2000

J. J. Wever et al.200

Fig. 3. Cross-sectional area at the suprarenal aortic neck in the 33 patients. Size in square millimetres is indicated on the vertical axis, andfollow-up interval for each patient is indicated on the horizontal axis.

betweentheavailablestent-graftdesigns. If theoutward Initial dilatation due to the procedure without sub-

sequent dilatation cannot be considered an adequateforce is the predominant cause of postoperative neck

dilatation, the diameter will probably not stretch bey- explanation, as the increase of the proximal neck area

was statistically significant for both the first and secondond the nominal (maximal) stent-size. But as the stent

approaches its maximal size, the friction forces between 6 months’ follow-up interval. No significant increase

of the suprarenal aorta was found in our study. Al-stentandaorticwallmaybecomedangerously low,with

possible stent migration as a result. The preferred graft though this provides some support of the theory that

progression of disease is not the only factor, it mustattachment design from this perspective would consist

of a stent with low outward force to prevent accelerated be realised that the infrarenal aorta has a less dense

fibre structure when compared to the suprarenaldilatation and a fixation mechanism independent of

friction forces between stent and neck (i.e. hooks). If aorta.14 No correlation could be found between the

presence or absence of endoleaks, pre- and post-progressive enlargement is merely a consequence of the

underlying aneurysmal disease, the oversizing of the operative neck-size, graft diameter and amount of

graft oversize, probably due to small numbers.stent graft relative to the neck-size actually allows the

stent to adapt to the neck dilatation. In this scenario, In conclusion, the infrarenal aortic neck dem-

onstrates continued dilatation after endograft place-high outward force would not necessarily be detri-

mental to the neck. Although it may take a longer period ment.

of time, the end-result of continued neck dilatation in

the presence of a stent with a limit to its diameter will

ultimately be the same: potential graft migration if noReferencesother fixation mechanisms are present. In addition, di-

latation beyond the nominal stent size may create a1 Sonesson B, Lanne T, Hansen F, Sandgren T. Infrarenal aortic

secondary attachment site leak, even without stent mi- diameter in the healthy person. Eur J Vasc Surg 1994; 8: 89–95.2 Lipski DA, Ernst CB. Natural history of the residual infrarenalgration.

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